When a dipped or cut-off beam or a fog penetrating beam is in use, the range of illumination afforded by the lamp is reduced, and this renders invisible or barely visible from any distance such things as road signs, route signposts, and/or warning signs of various kinds. Thus one of the objects of the present invention is to provide a headlamp with a chopped beam facility, in which this drawback is overcome.
It has already been proposed that motor vehicles can be equipped with headlamps which are adapted to emit only ultra violet radiation such as to enable road signs, of the kind having an outer coating that becomes fluorescent when subjected to ultra violet radiation, to be seen. One headlamp of that kind, for example that which is described in the specification of German published patent application No. DE 2 249 930A, is intended as an attachment for a lamp or a pair of lamps with which a motor vehicle is normally provided, in particular for headlamps having the illuminating functions normally referred to as dipped beam and main beam lighting.
Another headlamp is known from the specification of published International patent application No. WO 89/03778A, and consists of a dipped-beam headlamp which emits a light beam which is visible below a cut-off or chopping line, and which emits an ultra violet light beam above this cut-off line. A vehicle having a pair of headlamps in accordance with the above mentioned International patent application must, however, also have a further pair of headlamps which give a main or undipped beam.
In both of the prior art cases mentioned above, it is necessary to provide more than one pair of headlamps in order to obtain all the lighting functions necessary for a motor vehicle.